1. Field of the Invention
The present invention relates to a position measuring system, and more particularly, to a position measuring system with multiple bar mirrors for measuring a position of a stage and a mask in an exposure apparatus.
2. Description of the Prior Art
When manufacturing a liquid crystal display (LCD) panel, a photolithographic process and an etching process are used to define all kinds of electronic elements and optical elements (such as a color filter). Now, requirements for large-sized LCD panels are increased and a scanning exposure system is suitable for exposing large-sized substrates, so that the scanning exposure system is currently widely used in the photolithographic process.
Please refer to FIG. 10. FIG. 10 is a schematic diagram of a prior art scanning exposure system. As shown in FIG. 10, an exposure system 100 comprises a light source 102, a mask 104 positioned under the light source 102, and an optical system 106 positioned under the mask 104. Additionally, the mask 104 comprises a plurality of slits forming a predetermined pattern. The optical system 106 comprises a trapezoidal mirror 106a, a concave mirror 106b, and a convex mirror 106c located between the trapezoidal mirror 106a and the concave mirror 106b. The exposure system 100 further comprises a pedestal 108, a stage 110 positioned on the pedestal 108 in a movable way, and a substrate 112 positioned on the stage 110. The stage 110 is used to carry and move the substrate 112. A driving device (such as a linear motor) is used to control the stage 110 to move on the pedestal 108 in a magnetic levitation manner or an air-floating manner. Furthermore, the driving device also controls a moving direction of the stage 110 on the pedestal 108. The following description takes measuring a position of the stage 110 as an example.
For making the stage 110 move along a predetermined direction, a position measuring system is required to measure a moving direction of the stage 110. The position measuring system further transmits the measuring results to a control device, which can adjust the moving direction of the stage 110 adequately. Accordingly, the stage 110 is moved along the predetermined direction. Please refer to FIG. 11. FIG. 11 is a schematic diagram of a prior art position measuring system. As shown in FIG. 11, a prior art position measuring system comprises a stage 110, reflective mirrors 114, 116 disposed on the stage 110, laser interferometers 118a, 118b mounted beside the reflective mirror 114, laser interferometers 120a, 120b mounted beside the reflective mirror 116, and a control device 122. The laser interferometers 118a, 118b are used to measure a position of the stage 110 in the Y-axis direction, and the laser interferometers 120a, 120b are used to measure a position of the stage 110 in the X-axis direction.
Because a requirement of a large-sized liquid crystal display panel increases rapidly, it is necessary to manufacture a large-sized substrate 112. In the mean time, the size of the stage 110 in the exposure apparatus is increased due to the large-sized substrate 112. In order to precisely control the moving direction of the large-sized stage 110, lengths of the reflective mirrors 114, 116 are therefore prolonged. However, it is hard to manufacture a large-sized reflective mirror of a high quality through use of the present grinding technology. As a result, it is necessary to build a position measuring system with small-sized reflective mirrors capable of measuring a moving direction of a large-sized stage.